Research is being conducted to apply inter-vehicle communication technologies to a vehicle safety system, which aims to increase transportation efficiency and driving convenience. Inter-vehicle communication is performed at a previously allocated frequency band (for example, 5.9 GHz) when a plurality of vehicles are in a communication enabled area, which uses a short range communication technology (for example, Wireless Access in Vehicular Environment (WAVE) communication) based on Carrier sense multiple access with collision avoidance (CSMA/CA).
An inter-vehicle communication based vehicle safety system periodically broadcasts the position, speed, moving direction, and control information of the host vehicle to the surrounding vehicles in order to monitor traffic conditions around the vehicle in real time. Each vehicle predicts a collision situation on the basis of the driving information about the surrounding vehicles received through the inter-vehicle communication, to give a warning to the driver or surrounding vehicles if necessary.
FIG. 1 is a block diagram showing a related art inter-vehicle communication system.
A related art vehicle to vehicle (V2V) communication system includes an integrated information processing module 100, a sensor information reception module 110, a GPS signal reception module 120, and an inter-vehicle communication module 130.
The integrated information processing module 100 receives a sensing signal of a vehicle and a GPS signal from the sensor information reception module 110 and the GPS signal reception module 120, respectively, and then integrates, manages, and processes driving information (position, speed, driving direction, in-vehicle network information, driver manipulation information, etc.). The inter-vehicle communication system periodically (for example, for each 100 ms) broadcasts driving information about the host vehicle to the surrounding vehicles through the inter-vehicle communication module 130 (for example, WAVE).
The driving information about the surrounding vehicles received through the inter-vehicle communication module 130 is delivered to the integrated information processing module 100. The integrated information processing module 100 delivers the driving information about the host vehicle and its surrounding vehicles to an inter-vehicle safety service system 140 to perform functions such as risk degree determination, warning, etc.
FIG. 2 illustrates a channel load depending on surrounding conditions of a vehicle when the inter-vehicle communication is performed through a related art inter-vehicle communication system.
As illustrated in FIG. 2a, when a small number of vehicles travel around the host vehicle and thus the number of nodes communicating with the host vehicle is small, the channel load is so low that a data reception ratio increases and a channel access delay time decreases, thereby improving reliability of the system. However, as illustrated in FIG. 2b, when there are a lot of surrounding vehicles, i.e., a lot of nodes communicating with the host vehicle, the channel load is so high that the data reception ratio decreases and the channel access delay time increases, thereby deteriorating the reliability of the system.
The CSMA/CA based wireless communication technology, which is used to periodically broadcast driving information to surrounding vehicles, has a problem in that a data transmission success rate is reduced due to frequent variation in network topologies caused by high mobility of vehicles, data collision caused by hidden node problem, etc.
Furthermore, the CSMA/CA based wireless communication technology has a network congestion problem where transmission delay and data loss increase dramatically due to excessive competition between nodes when there are an enormous number of inter-vehicle communication nodes (for example, downtown intersection, highway bottleneck) and does not have a function of managing transmission power, data transmission rate, and data transmission period depending on wireless channel states in order to solve the network congestion problem in the inter-vehicle communication.